1. Field of the Invention
This invention relates to noncuring transparent organopolysiloxane compositions useful as coupling agents or fillers for optical communication components.
2. Background Information
Organopolysiloxane compositions of organopolysiloxane and finely particulate silica are generally called silicone compounds and are used for diverse applications such as lubricants, sealants, release compounds, and fillers due to their excellent heat resistance, cold resistance, weather resistance, lubricity, nonflowability, electric insulation, and water repellency. However, in such silicone compounds, the index of refraction of the organopolysiloxane is different from the index of refraction of the fine powder, for example, n.sub.D.sup.25 =1.4040 for dimethylpolysiloxane while n.sub.D.sup.25 =1.430 for finely particulate silica (where n.sub.D.sup.25 is the index of refraction at 25.degree. C. here and below) and they are opaque due to diffuse reflection at the solid's surface. Such silicone compounds exhibit a poor light transmittance of 90% or less at a wavelength of 500 nm.
As a result, organopolysiloxanes containing the phenyl radical have been introduced in order to increase the index of refraction of the organopolysiloxane up to that of the finely particulate silica and thus to improve the transparency of the resulting silicone compound. However, the resulting silicone compounds suffer the restriction that, with a n.sub.D.sup.25 of approximately 1.43, they cannot be used as binder fillers for optical communication elements with an optical component with a n.sub.D.sup.25 of 1.45 to 1.48. Liquid organopolysiloxanes with a n.sub.D.sup.25 of 1.45 to 1.48, known as matching oils, have been used in the prior art as binder fillers for such optical communication elements; however, they present the drawback of flowing out of the filled part due to their fluidity.
Various methods were examined by the present inventor for the purpose of eliminating the above drawbacks and a transparent organopolysiloxane composition with an index of refraction of 1.45 to 1.48 at 25.degree. C. and an insignificant fluidity was discovered as a result.